Meteorite classification for building the Chinese Antarctic Meteorite Depository Introduction of the classification of 500 Grove Mountains meteorites

Meteorites provide an important window into the origins and evolution of the solar system. Since the first four meteorites were recovered in Grove Mountains, Antarctica, in 1998, a further total of 12665 meteorites have been collected over seven polar seasons in the Grove Mountains. All of these meteorites are owned and managed by the Chinese Antarctic Meteorite Depository （CAMD） at the Polar Research Institute of China （PRIC）. In recent years, another 500 Antarctic meteorites have been classified and characterized based on mineralogy and petrology. In this work we examine four samples that have been identified as terrestrial, and a further 496 samples that have been confirmed as meteorites. These meteorites are further divided into different types：488 ordinary chondrites, one eucrite, one ureilite, one CM2 carbonaceous chondrite, one EH4 enstatite chondrite, one mesosiderite and three iron meteorites. The classification of meteorites not only provides an abundance of fundamental scientific data, but is also significant for introducing meteorites and related scientific knowledge to the publics particularly via the website of Chinese Resource-sharing Platform of Polar Samples for scientific research and education.

Shock metamorphism of ordinary chondrites from Grove Mountains,Antarctica

Shock effects of 93 Grove Mountains （GRV） ordinary chondrites were studied in this work, including fracture, various types of extinction, and recrystallization of silicates observed under optical microscopy. Shock-induced veins and pockets show various microtextures, decomposition and phase transformation of minerals. The confirmed high-pressure polymorphs of silicates are ringwoodite, majorite, pyroxene glass and maskelynite. Based on the shock effects and assemblages of high-pressure minerals, shock stages of all of 93 GRV ehondrites were classified. In comparison with literature, the Grove Mountains meteorites have a higher fraction （23 out of 93 ） of heavily shocked samples （S4--S5）. Most of the heavily shocked meteorites are L group （22 out of 23）, except for one H chondrite. The distinct shock metamorphism between H and. L groups may indicate different surface properties of their parent bodies. In addition, there is relationship between petrologic types and shock stages, with most heavily shocked samples observed in equilibrated ordinary chondrites （ especially Type 5 and 6）.

Response of silicate chemical composition variation on thermal metamorphism of ordinary chondrites and classification of petrologic types:the case of L chondrites from Grove Mountains,Antarctica

Analysis of the thermal metamorphism of the ordinary chondrites is a key premise for gaining insights into the accretion and heating of rocky bodies in the early solar system.Such an analysis also represents an essential condition for constraining the early thermal and evolutionary histories of asteroids and terrestrial planets.Classifying ordinary chondrites into petrologic type(type 3–6)is the criterion for studying the thermal metamorphism of their parent bodies.However,the boundary between the unequilibrated(type 3)and equilibrated(type 4–6)chondrites is ambiguous at present,thus,limiting the understanding of their thermal metamorphism.In this study,the petrology,mineralogy and chemical composition of a set of seven ordinary chondrites with different degrees of thermal metamorphism collected from Grove Mountains(Antarctica)have been studied.The results demonstrated that these chondrite samples were L3.7,L3.8,L3.9,L3.9/4,L4,L5 and L6 type meteorites,with optimal correlations of Si,Mg,Fe,Mn and Ca with equilibrium degree of the olivine and low-calcium pyroxene and petrologic type.In this respect,the multi-parameter classification standard PMD(SiO2)-PMD(MgO)-PMD(MnO)-PMD(CaO)based on the percent mean deviation(PMD)of the chemical compositions of the olivine and low-calcium pyroxene was proposed to distinguish between the unequilibrated and equilibrated meteorites.The proposed standard exhibited high“resolution”in terms of classification,thus,also deepening the understanding of the effect of the silicate mineral composition in the thermal metamorphism of chondrites.Highlights The chemical groups and petrologic types of the selected seven Antarctic chondrites were L3.7,L3.8,L3.9,L3.9/4,L4,L5 and L6.A new method for petrologic type classification is proposed to distinguish the unequilibrated and equilibrated chondrites.The above developed multi-parameter system exhibited high“resolution”in terms of classification.

GPR Surveying in the kernel area of Grove Mountains,Antarctica

The Grove Mountains, located between the Zhongshan Station and Dome A, are a very important area in inland Antarctic research. China has organized ifve investigations of the Grove Mountains, encompassing the geological structure, ancient climate, meteorites, ice-movement monitoring, basic mapping, meteorological observations, and other multi-disciplinary observational studies. During the 26th Chinese National Antarctic Research Expedition in 2010, the Grove Mountains investigation team applied specialized ground-penetrating radar （GPR） to survey subglacial topography in the eastern kernel area of the Grove Mountains. In this paper, we processed GPS and GPR data gathered in the ifeld and drew, for the ifrst time, two subglacial topographic maps of the Grove Mountains kernel area using professional graphics software. The preliminary results reveal the mystery of the nunatak landform of this area, give an exploratory sense of the real bedrock landforms, and indicate a possible sedimentary basin under the Pliocene epoch fossil ice in the Grove Mountains area. Additionally, it has been proven from cross-sectional analysis between Mount Harding and the Zakharoff ridge that the box-valley shape between two nunataks has already matured.

Chemical compositions and cassfication of Grove Mountains(GRV)98003 and other Chinese iron meteorites

Concentrations of Cr, Co, Ni, Cu, Ga, Ge, As, Sb, W, Re, Ir, Pt and Au of two ungrouped iron meteorites, Grove Mountains （GRV） 98003 from Antarctica and Ujimqin, were measured using instrumental neutron activation analysis. According to the bulk chemistry, GRV 98003 is classified as a member of ⅠAB group, and Ujimqin as a unique one of ⅠAB iron meteorite complex. The elemental abundance pattern and correlation between elements （e. g. Ni-Au, Co-Au, As-Au, W- Au, Cu-Au, Sb-Au） of GRV 98003 are similar with those of NAW 468 （ⅠAB）, but significantly depleted in refractory siderophile elements （ Re, It） and moderate volatile elements （Ca, Ge） relative to the latter. In addition, we reclassify Nantan （ⅢCD） as a member of ⅠAB main group （MG） and Yongning （ⅠA） as a unique iron meteorite related with IAB iron meteorite complex.

Preliminary study on the spore-pollen assemblages found in the Cenozoic sedimentary rocks in Grove Mountains,east Antarctica and its climatic implications

Glaciogene sedimentary rocks have been found in modem tills of the Grove Mountains, east Antarctica during the 1998 - 1999 Chinese National Antarctic Research Expedition （CHNARE）. Based on the lithilogic and sedimentary features, these sedimentary rocks are correlated with Cenozoic sedimentary strata of the Pagodroma Group in the neighboring Prince Charles Mountains and the Sorsdal Formation in VestFold Hills. Sedimentary clasts contain sparsely Late Tertiary spores and pollens, including ： Toroisporis （ Lygodiaceae）, Osmunda, Granulatisporites （ Pteridaceae？） , Polypodiaceae, Podocarpus , Araucariaceae, Artemisia , Rhus , Nothofagidites , Proteacidites （Proteaceae） , Quercus , Fraxinoipollenites （ Oleaceae ） , Oleoidearumpollenites（ Oleaceae ）, Operculumpollis, and Tricolpopollenites. Most of the pollen and spores contained in these samples originate from local sources according to the conditions of their preservations as well as correlations with the microfossil assemblages found in the neighboring areas. The majority of the pollen assemblages, as represented by Podocarpus and Nothofagus, belong to the Weddellian biogeocenose, however some exotic components from the old sedimentary basement rocks may have been included during erosion of the proximal ice sheet. If the source areas of glaciogenic sedimentary rocks that bear the pollen and spores are assumed to be local, or in the up glacier areas, the pollen assemblages in these samples might represent an inland flora during a warmer period of the ice-sheet evolutionary history. The finding of the Artemisia and Chenopodiaceae in the pollen assemblages implies that they may belong to late Tertiary （most probably Pliocene）. The absence of diatoms in the samples analyzed may indicate that there are no Cenozoic marine strata in the interior of the east Antarctica beyond the Grove Mountains. The significances of the finding of the Nothofagus in these pollen assemblages are discussed on the basis of current knowledge about the age, distribution and ecological conditions of this kind of fossils found in Sirius Group or other strata outcropped in Antarctica. As a preliminary conclusion, we think that the existence of the Cenozoic glaciogenenic rocks and their pollen assemblages present new evidence for a large scale glacial retreat history in Grove Mountains of east Antarctica, and thus support a dynamic East Antarctic Ice Sheet （EAIS）. This is consistent with the interpretations of Webb et al. （1984）.

Classification of Grove Mountains meteorites and its significance

Meteorites are the extraterrestrial rocks, which provide insights into the origin and evolution of the solar system. During the past half century, a great number of meteorites has been discovered on the Antarctic Ice Sheet, confirming that the Antarctica is the most important meteorite concentration area on the earth. Since the first four Antarctic meteorites were found in Grove Mountains in 1998, a total of 9834 meteorites have been collected by four subsequent expeditions. It opens a new field of meteorite study in China, and also accumulates a great deal of scientific samples for China. Recently, classification of Grove Mountains meteorites has been carried out for 6 years, and made following progresses ： （ 1 ） 2433 meteorites, which include many special meteorites, e.g. Martian meteorites, ureilites and carbonaceous chondrites, have been classified. （2） the Antarctic meteorite curation and the sample sharing system are set up preliminarily. （3） the classification procedure, the management of meteorite samples, and the application procedure for the Antarctic meteorites are completed after the systematic classification during these years. （4） young generation researchers on meteorite are trained through the cooperation of many universities and institutes on meteorite classification.

U-Th-Pb monazite and Sm-Nd dating of high-grade rocks from the Grove Mountains, East Antarctica: further evidence for a Pan-African-aged monometamorphic terrane

The Grove Mountains, 400 km south of the Chinese Antarctic Zhongshan Station, are an inland continuation of the Pan-African-aged （i.e., Late Neoproterozoic/Cambrian） Prydz Belt, East Antarctica. In this paper we carried out a combined U-Th-Pb monazite and Sm-Nd mineral-whole-rock dating on para- and orthogneisses from bedrock in the Grove Mountains. U-Th-Pb monazite dating of a cordierite-bearing pelitic paragneiss yields ages of 523 ？ 4 Ma for the cores and 508 ？ 6 Ma for the rims. Sm-Nd mineral-whole-rock isotopic analyses yield isochron ages of 536 ？ 3 Ma for a coarse-grained felsic orthogneiss and 507 ？ 30 Ma for a fine-grained quartzofeldspathic paragneiss. Combined with previously published age data in the Grove Mountains and adjacent areas, the older age of ~530 Ma is interpreted as the time of regional medium- to low-pressure granulite-facies metamorphism, and the younger age of ~510 Ma as the cooling age of the granulite terrane. The absence of evidence for a Grenville-aged （i.e., Late Mesoproterozoic/Early Neoproterozoic） metamorphic event indicates that the Grove Mountains have experienced only a single metamorphic cycle, i.e., Pan-African-aged, which distinguishes them from other polymetamorphic terranes in the Prydz Belt. This will provide important constraints on the controversial nature of the Prydz Belt.

Petrology of ureilites from Grove Mountains,Antarctica:Constraints on the origins

Ureilites are a common group of achondrites with a high abundance of carbon. They probably have a genetic relationship with chondrites, hence provide an insight into origin and evdution of terrestrial planets. A new meteorite-rich region, Grove Mountains （ GRV）, was found by the Chinese Antarctic Research Expedition, with discovery of 9834 meteorites. Of 2433 meteorites classified, 9 ureilites have been identified. In this paper, we report petrography of 6 of these ureilites. Four ureilites contain graphite and exhibit triangle conjunction and common reduced margins of divine. GRV 052382 probably experienced heavy shock metamorphism followed by fast coding, as indicated by mosaic texture or fine-grained granular texture of olivine. GRV 022931 was highly reduced of these ureilites, with olivine as isolated grains in abundant carbonaceous matrix. All 9 ureilites are monomict, and arc classified into subtype II （with medium FeO content, Fa15-18 ） and subtype I （with high FeO content, Fa 〉 18） based on compositions of the cores of olivine. The diverse mineral compositions and petrography of these ureilites suggest that they are not paired and reveal a multi-event history of the parent body. Partial melting of the parent body produced carbon-rich magma, followed by crystallization of graphite and silicates. Later, graphite was partially inverted to diamond by shock events. Reburial of the shocked debris experienced various degree of thermal metamorphism. Finally, these rocks were excavated from the parent asteroid and ejected into Earth-cross orbit by another impact event.

Preliminary investigation of rubidium distribution in the Grove Mountains area, East Antarctica

We analyzed rock samples from the Grove Mountains in Antarctica to determine the distribution of rubidium （Rb） in that location. We collected samples from the Black Nunataks, Melvoldt Nunataks, Mason Peaks, Zakharoff Ridge, Mount Harding, and the northern Gale Escarpment. Geochemical analysis indicated that in some samples the amount of Rb was higher than 300 ppm. This suggests that rocks from the Grove Mountains are rich in Rb. Based on field observations and previous research, we speculate that mica and potash feldspar from moyite, granite gneiss, and felsic pegmatite are the primary carrier minerals of Rb. However, further research is necessary to confirm this speculation.

Elevation determination of nunataks in the Grove Mountains

A majority of the exposed nunataks located in the Grove Mountains of the Antarctic interior have yet to have had their elevations measured. The elevations of Mason Peak and Wilson Ridge were precisely determined by the Grove Team of the 26th CHINARE in 2010, with Mason Peak turning out to be the highest of the Grove Mountains. Considering that both Mason Peak and Wilson Ridge are difficult to climb because of their cragginess, we first selected three control points on the ice surface near Mason Peak and positioned them with GPS. Thus, accurate elevations of Mason Peak and Wilson Ridge could be calculated from three directions using forward intersection and trigonometric leveling of a high-precision theodolite at the chosen control points. The results provide basic geodetic information that can be referred to as high-precision control points for surveying and mapping in this part of Antarctica. This paper elaborates on the process of measurement and computation of the mountains summit elevations, and also analyzes the details of the principal elements influencing the accuracy of trigonometric leveling, the determination of refraction coefficients k, and observations of structure and distance.

Shock effects and the classification of H-chondrites from the Grove Mountains,East Antarctica:Implications for the shock history of H-chondrite parent bodies

The shock metamorphism of 47 H group chondrites （H-chondrites） from the Grove Mountains including undulatory extinction, planar fractures, mosaic extinction, shock veins and pockets, and dendritic eutectic metal-sulfide, is observed through optical microscope. The textures and assemblages of shock veins in these H-chondrites are examined by the scanning electron microscope. Based on observations of the above shock effects, the shock stages of the 47 H-chondrites are classified into S1（5）, S2（19）,S$3（14）, S4（8） and S5（1）. Of these H-chondrites, GRV 022469 has the highest（S5） shock stage. The comparison of shock stages in these H-chondrites with L group chondrites（L-chondrites） indicates that the shock metamorphism of H-chondrites is relatively low （except for GRV 022469, they are all lower than $5）. A scenario for the history of the H-chondrite parent body is proposed that suggests the duration of the shock events in the H-chondrite parent bodies was much shorter than those in L-chondrite parent bodies. Also, the pressure may have been released more quickly, and consequently, the high-pressure phases should be easily preserved. However, the parent bodies of the H-chondrites may have been exposed to high temperatures for a longer time after the shock event, so the high-pressure phases formed by solid transformation might have retro-metamorphosed to low-pressure ones; its peak pressure is estimated to be less than 15 GPa. Wadsleyite was found in a shock vein in GRV022469, as confirmed by the Raman spectrometer. Petrological and mineralogical characteristics support the idea that the wadsleyite was formed by solid-state transformation.

The digital mapping of satellite images under no ground control and the distribution of landform, blue ice and meteorites in the Grove Mountains, Antarctica

The colorful satellite image maps with the scale of 1∶100000 were made by processing the parameters-on-satellite under the condition of no data of field surveying. The purpose is to ensure the smooth performance of the choice of expedition route, navigation and research task before the Chinese National Antarctic Research Expedition (CHINARE) first made researches on the Grove Mountains. Moreover, on the basis of the visual interpretation of the satellite image, we preliminarily analyze and discuss the relief and landform, blue ice and meteorite distribution characteristics in the Grove Mountains.

The establishment of GPS network in Grove Mountains,East Antarctica

The Grove Mountains are located in Princess Elizabeth Land, East Antarctica, extending from 72° to 73°S latitude and 73° to 76°E longitude, covering approximately 8000 km^2 areas. During the 2002/2003 austral summer season, the 19th CHINARE （Chinese National Antarctic Research Expedition） carried out the third expedition in Grove Mountains, East Antarctica. The Geodetic network was established, which can provide ground control for the satellite image map for the multi-discipline expedition in the Grove Mountains where seven permanent GPS benchmarks were set up supported by the helicopter and snow vehicles. All GPS sites besides Z001 were observed at least for one hour using the dual frequencies Trimble 4000ssi GPS receivers. The data were processed by the comprehensive GPS analysis package--GAMIT/GLOBK and the precision is good enough to satisfy with the acquirement of satellite mapping in this area.

Preliminary study on the erratic exposure ages of Grove Mountains,East Antarctica

The first study of erratic boulder exposure ages in the Grove Mountains, interior Antarctica, indicates the two erratic boulders （060131-1 and 060131-2, collected from a typical nunataks, Zakharoff Ridge in the Grove Mountains） have 10 Be minimum exposure ages of 1.24 ±0. 11 Ma, 1.37 ±0. 12 Ma, and ^26Al ages of 0.90 ±0.12 Ma,0.44 ±0.04 Ma, respectively. Meanwhile, another erratic boulder sample 060131-4, coming from vicinal ice surface, has ^10Be and ^26Al minimum exposure ages of 0.47 ±0.3 Ma and 0. 44 ±0.04 Ma, respectively. The exposure ages of the three erratic boulders are nearly similar to the bedrocks with the similar elevation. Thus, using the technique of in situ produced terrestrial cosmogenic nuclides, the ice sheet evolution histories in the Grove Mountains reflected by erratic boulder and bedrock exposure ages are basically consistent.

Evidence for warmer event from quartz grains in the soil of Grove Mountains,East Antarctica

The cold desert soll has been discovered at first time in southern ridge of Mount Harding, Grove Mountains of interior East Antarctica Ice Sheet. Based on the micro structural observation, dominant characteristics of quartz grains include： distinct surface stria and fractures, and clean features of frost action at both of crystal margins and micro crannies of quartz grains. These features show a pedogenesis environment of few water, short transportation and frost action, revealing a warmer climatic event existed in this re, on.

Summer weather characteristics on the Grove Mountain of East Antarctica

The summer weather characteristics of the Grove Mountain, East Antarctica, are presented based on the data obtained by Chinese National Antarctic Expedition (CHINARE) in January 1999. The result shows that the pattern of daily variation of temperature and the prevailing wind direction in Grove is similar to that of Zhongshan Station. However, the daily range of temperature and strong wind frequency are much higher than those of Zhongshan Station.The change of wind direction is close to the weather system that impacted the Grove Mountain. The warm and wet air from northern parts often causes the precipitation. The clear weather appears when controlled by eastern winds in January.

Geology of the Grove Mountains in East Antarctica——New evidence for the final suture of Gondwana Land

Grove Mountains consists mainly of a series of high-grade (upper amphibolite to granu-lite facies) metamorphic rocks, including felsic granulite, granitic gneiss, mafic granulite lenses and charnockite, intruded by late tectonic gneissic granite and post-tectonic granodioritic veins. Geo-chemical analysis demonstrates that the charnockite, granitic gneiss and granite belonged to aluminous A type plutonic rocks, whereas the felsic and mafic granulite were from supracrustal materials as island-arc, oceanic island and middle oceanic ridge basalt. A few high-strained shear zones disperse in regional stable sub-horizontal foliated metamorphic rocks. Three generations of ductile deformation were identified, in which D1 is related to the event before Pan-African age, D2 corresponds to the regional granulite peak metamorphism, whereas D3 reflects ductile extension in late Pan-African orogenic period. The metamorphic reactions from granitic gneiss indicate a single granulite facies event, but 3 steps from mafic granulite, with P-T condition of M1 800℃, 9.3×105 Pa; M2 800—810℃, 6.4×105 Pa ; and M3 650℃ have been recognized. The U-Pb age data from representative granitic gneiss indicate (529±14) Ma of peak metamorphism, (534±5) Ma of gran-ite emplacement, and (501±7) Ma of post-tectonic granodioritic veins. All these evidences sug-gest that a huge Pan-African aged mobile belt exists in the East Antarctic Shield extending from Prydz Bay via Grove Mountains to the southern Prince Charles Mountains. This orogenic belt could be the final suture during the Gondwana Land assemblage.

Type distribution pattern and pairing of ordinary chondrites from Grove Mountains,Antarctica

Twenty-eight meteorites were collected on blue ice in the Grove Mountains region, Antarctica, by the 16th Chinese Antarctic Research Expedition (CHINARE). 26 out of the stones are ordinary chondrites, and their chemical-petrographic types are assigned based on electron probe microanalyses, petrography and mineralogy. 6 of them are unequilibrated L-chondrites, and the other 20 chondrites are equilibrated, including 6 H-group (3 H4, 1 H5 and 2 H6), 9 L-group (3 L4, 1 L5 and 5 L6) and 5 LL-group (2 LL4 and 3 LL5). Detailed comparative study suggests that 10 of them (including other 2 chondrites collected by the 15th CHINARE) could be paired, and represent 5 individual fall events. Hence, all 32 meteorites collected from the Grove Mountains probably belong to 27 fall events, suggestive of meteorite transferring and concentrating processes. The Grove Mountains are likely a new meteorite-enriched region. Distribution patterns of chemical-petrographic type and mass of the Grove Mountains meteorites are significantly distinct from those found in other regions, indicative of their unique sources and/or concentration mechanism. However, more studies are required in order to clarify these differences.

DINSAR measurement of glacier motion in Antarctic Grove Mountain

Grove Mountain is an important nunatak region on East Antarctic Glacier that blocks the ice flow to- ward Lambert Glacier. The existence of nunataks and subglacial mountains leads to complex ice flow patterns, which are difficult to be measured by conventional ground-based methods. In this study, several JERS-1 and ERS-1/2 SAR images covering this area are used for 3-pass and 4-pass differential interferometric processing. The ice flow field of Grove Mountain and the eastern zone are derived and validated with related knowledge. The research shows that DINSAR is an effective method for meas- uring complex ice flow in Antarctic inland glacier. L-band DINSAR is more suitable for mid or fast ice flow than C-band over this region.